OUR STUDIES ON THE ACIDIFICATION OF THE VAS DEFERENS FORMED ROUND THE COMMON INTEREST OF DRS. SMITH AND BROWN IN THE PHYSIOLOGICAL ROLE OF THE VACUOLAR-TYPE PROTON ATPASE. RESULTS HAVE BEEN EXTREMELY ENCOURAGING WITH PROBE DATA SUPPORTING IMMUNOHISTOCHEMICAL STUDIES IN ATTRIBUTING A MAJOR ROLE TO THESE PUMPS IN REGULATING MAMMALIAN SPERM ACTIVITY. THUS, THE V-TYPE PROTON PUMPING ATPASE IS IMPLICATED AS THE MAJOR SOURCE OF THE LUMINAL ACIDIFICATION IN PARTS OF THE MALE REPRODUCTIVE TRACT. THIS ENZYME IS LOCATED IN A MINORITY CELL TYPE, WHICH RESEMBLES THE ACID-SECRETING INTERCALATED CELL OF THE RENAL COLLECTING DUCT. FURTHER DETAILS ARE GIVEN IN HIGHLIGHTS. THIS PROJECT HAS NOW BEEN JOINED BY DR. BRETON AS POSTDOCTORAL FELLOW IN DR. BROWN~S LAB.